Germany’s Energiewende – the energy transition – is posing significant challenges for the existing electricity grid. The increasingly decentralised and temporally fluctuating production of electricity from renewable sources makes it necessary to create additional transport capacity for electrical energy. With critical components for the energy transmission, thermal and electrical phenomena depend heavily on each other and determine the current-carrying capacity. Under the direction of Professor Andreas Küchler, Professor Johannes Paulus, Professor Markus H. Zink and graduate engineer Achim Langens, the joint Trans-HK project is concerned with developing methods for producing thermoelectrically coupled simulations of electrically and thermally highly stressed components. The project partners will then verify these methods using precise replicas of bushings and transfer them to other critical components used for transferring energy.

As one of their main objectives, the scientists want to increase and secure the transport capacity of three-phase systems and DC transmission lines. This can be achieved through analysing critically stressed high-voltage components. These include, for example, transformer bushings, wall bushings, cables, cable sleeves, cable terminations or cable taps and so-called J-tubes. The strongly coupled thermal and electrical phenomena in these components limit the current-carrying capacity of the components, the associated equipment and ultimately the whole transmission chain.

The problems with high-voltage alternating current transmission (HVAC) are somewhat different from those with high-voltage direct current transmission (HVDC): with AC voltage the thermal stresses that are also partly determined by the dielectric properties of the insulation play a major role. With DC voltage, on the other hand, there is a risk of electrical overloads caused by thermally induced field shifts.

The outcome of the project will comprise simulation methods that record the mutual thermoelectric coupling for the components considered, which have been experimentally verified on one component, and which can be applied to all the components. These methods are aimed at optimising the components for the energy transmission chain, whereby it is expected that these will also make a considerable contribution to understanding the physical processes that could lead to the failure of insulation systems and thus the failure of the transmission chain. In addition, where appropriate the unused potential of existing components can also be identified, thus reducing the need for building additional capacities.

The milestones at a glance

Research and planning – vulnerabilities in the power transmission chains are determined and, based on them, a work plan created.

Mock-ups for the experimental verification of simulation models – components are selected and a suitable simulation method determined. The HSP project partner will then construct downscaled mock-ups.

Verification of separate thermal and electrical simulation models – electric and thermal loads are simulated separately and compared with laboratory measurements. This enables the modelling to be verified.

Verification of coupled thermoelectric simulation models – the coupled thermoelectric simulation is then in turn verified using the mock-ups.

Simulation of critically loaded components – the determined vulnerabilities enable the risks to be determined. In addition, existing reserves will be identified and quantified. Ultimately it will be possible to derive proposals for optimising the components.

The tasks of the project partners

At Würzburg-Schweinfurt University of Applied Sciences (FHWS), four participants in particular are specifically involved in the project: the Institut für Energie- und Hochspannungstechnik IEHT is coordinating the project; the laboratory for thermal engineering and thermodynamics is conducting thermal measurements of the materials as well as thermal and coupled simulations; high-voltage technical tests and dielectric measurements of the materials are being conducted in the high-voltage engineering laboratory, while the laboratory for dielectric diagnostics and simulations is also carrying out dielectric measurements of the materials as well as electrical and coupled simulations.

Several project participants are also involved at the industrial partner, HSP Hochspannungsgeräte GmbH: the technical management is responsible for the coordination while the technology and development departments are providing the material data and test samples and are also preparing the production of test objects and original bushings. The production is responsible for manufacturing the objects close to reality. Electrical and thermal tests in the test fields are used to verify the methods.